searching for a broker and a demo account

im getting ready to trade s&p futures via the internet. i have a starting capital of 15,000 dollars. i have chosen ninja trader as my trading platform, and now i want to find a good broker with low commissions, no monthly fees, etc. which one do u recomend me?

and also i am looking for a demo acount of at least 6 months length, so i can practice enough to start to trade with real money, and all the demo accounts i have seen in the internet only last 2 weeks or 1 month. do u know any demo account with longer length?